Wafer-scale integration refers to the processing of semiconductor wafers to have a multitude of discrete devices which are interconnected and whereby the wafer will not be diced. Major subsystems and even entire computers could be built on a single, undiced, standard-size wafer. The area separating the multitude of single discrete units on a wafer for a wafer-scale integration is commonly referred to as "street area".
The concept of "yield" is of great concern to semiconductor processing facilities. Overall yield is the percent of usable assembled packages as compared to the number of individual dies mapped on a wafer at the start of the process. Wafer fabrication requires a high degree of precision. One mistake can render an individual die or perhaps an entire wafer completely useless. Therefore, as the wafer proceeds through fabrication processing steps, it undergoes a variety of tests and evaluations to evaluate operability.
Yield is typically significantly below 100%, the result of wafer breakage, process variations, or process defects. In fabricating wafers to be diced, the good, usable dies are collected and assembled into packages, and the defective dies discarded. The finished product after assembly is tested to assure that working product is being shipped.
With wafer-scale integration, the concept of yield becomes even more critical and is a significant reason why successful wafer-scale integration has substantial eluded the electronics industry. Critical defects on a wafer that will not be diced effectively result in a wafer that is entirely unusable. As yields typically do not approach near 100% for a given wafer, significant redundancy would have to be built into the respective discrete components on the wafer. Circuitry must then be provided to identify and isolate nonworking components, and to provide appropriate interconnection of the working components on a single wafer.
It is desirable to maximize yield in wafer-scale integration and utilize as much of the space on the wafer as possible for circuitry.